1. General Nature of the Invention
This invention relates to porous electrodes for use in electrochemical cells, particularly for use in fuel cells.
2. Description of the Prior Art
A known kind of electrode which is particularly suitable for use in fuel cells comprises a porous layer containing carbon and a non-polar resin and an electrically conducting lattice-work acting as a collector. Such an electrode is described in the published Netherlands patent application No. 72 14900.
During operation the fuel used penetrates into the pores of the porous layer, which usually contains a catalytically active material that catalyses the galvanic combustion of the fuel in the porous layer. The generation of electric current occurs in the porous layer and the current generated is collected by the electrically conducting lattice-work, and led off therefrom. The electorde is in contact with a suitable electrolyte which closes the circuit within the fuel cell and by which the reaction products of reactions occurring at the cathode and anode can also be led off.
A particular disadvantage of known porous fuel-cell electrodes is the detachment of the collector which occurs during operation, e.g. as a consequence of corrosion, which collector consists in practice of, for example, metal gauze with a wire thickness of approximately 150 .mu.m and a mesh size of approximately 700 .mu.m, or a correspondingly perforated metal plate. Expanded metal may also be used as a collector. As a result of the corrosion the internal resistance of the electrode increases and the strength of adhesion between the collector and the porous layer decreases. This adhesive strength may decrease even after a relatively short operating time so that the porous layer detaches from the collector and the electrode becomes completely unusable.
To suppress the corrosion, the collector is made of corrosion-resistant metals such as nickel, silver, gold or platinum. Usually nickel is used, as this is the least expensive. Nickel however is not completely free from the disadvantages referred to.
It has previously been suggested in U.S. Pat. No. 3,671,317 to incorporate in an electrode a metal lattice-work which, in order to combat corrosion, is surrounded by an enclosing layer of a thermoplastic material, e.g. polyvinylidene fluoride, with around it, a layer of fluorocarbon polymer, e.g. polytetrafluoro-ethylene, containing conductive particles such as carbon. In such a construction however the metal lattice-work does not act as a collector and this results in a very high internal resistance of the electrode and unfavourable efficiency of current generation.
It has also previously been proposed in French patent specification No. 2,215,710 to affix the collector to the porous layer by means of a synthetic lacquer, e.g. an epoxy resin containing graphite. However, the side of the collector not treated with the lacquer remains exposed to corrosion.